1. Field of the Invention
The present invention relates to an image display medium, an image display device and an image display method, and particularly to an image display medium capable of implementing repeatedly rewritable display by moving colored particles with an electric field, to an image display device equipped with the image display medium and to an image display method therefor.
2. Description of the Related Art
Heretofore, methods have been proposed in which a dispersion fluid in which colored particles are dispersed is enclosed between a transparent display plate and a rear face plate, the colored particles are arbitrarily moved by forming electric fields between the plates in accordance with image information, and color of the colored particles, color of the dispersion fluid and/or color of a colored rear face plate is displayed.
For example, Japanese Patent Application Laid-Open (JP-A) No. 9-185087 discloses a structure in which, as shown in FIG. 40A, a dispersion in which black particles 4 are dispersed in a white dispersion fluid L is employed, the black particles 4 are adhered to a transparent display plate 1 side, to implement black display, by an electric field which is formed between the plates by a voltage applied between an electrode 7a and an electrode 7b. Conversely, as shown in FIG. 40B, white display is implemented by moving and adhering the black particles 4 to a rear face plate 2 side.
Further, JP-A No. 2003-107532 discloses a structure which, as shown in FIGS. 41A and 41B, employs a dispersion in which white particles 5 and the black particles 4, which have different electrostatic polarities, are dispersed in a transparent dispersion fluid L, and the white particles 5 and black particles 4 are selectively adhered to the display plate 1 side to implement display by an electric field formed between the plates by a voltage applied between the electrodes 7a and 7b. 
Further still, JP-A No. 11-202804 discloses a structure in which, as shown in FIG. 42A, a dispersion in which the black particles 4 are dispersed in a transparent dispersion fluid L is employed, and a colored layer 6 on the rear face plate 2 is colored white. Hence, white display is implemented by removing the black particles 4 from above the colored layer 6 by an electric field which is formed by a voltage applied between the electrodes 7a and 7b and, as shown in FIG. 42B, black display is implemented by adhering the black particles 4 to the colored layer 6.
These image display mediums, being reflection-type image display mediums, are capable of providing high whiteness and black-white contrast, and have been anticipated as image display mediums that implement displays comparable to paper.
However, in these systems, only two colors can be displayed at a single display element, and consequently multi-color display cannot be implemented by the basic forms. Accordingly, methods of forming color filters at a display surface for multi-colorization, methods which employ chromatic particles, methods in which the rear face plate is colorized, and the like have been investigated (see, e.g., JP-A No. 2000-347483).
A method which employs color filters displays an arbitrary color by mixing a color of particles adhered to an inner face of the display plate with the color filter formed at the display plate. For example, if the image display medium employs white particles and black particles, the color of the color filter is displayed when the white particles are adhered to the display plate, and black display is implemented when the black particles are adhered thereat. Here, it is possible to employ an RGB filter as the color filter, control the reflection of red, green and blue light by moving the white particles and black particles in accordance with image information, and hence display arbitrary colors.
However, if a color filter is disposed at the display plate, there is a problem in that whiteness, which is a particular feature of these image display mediums, is lost and backgrounds of displayed images are darkened.
Further, with a method which employs chromatic particles, for example, red, green and blue particles or a combination of dispersion fluids of each color with black particles are enclosed in cells with a regular arrangement, and one pixel is formed by three neighboring cells.
However, although black display by the black particles is excellent, white display is implemented by combining the colors of the colored particles. Therefore, there is a problem in that display density is higher, and whiteness is lost.
Furthermore, with a combination of red, green and blue particles with white particles, white display by the white particles is excellent, but black display is implemented by combining the colors of the chromatic particles. Consequently, there is a problem in that display density is reduced.
Further again, with a method in which the rear face plate is colorized, respective cells at the rear face plate are colored, for example, red, green and blue, and these are combined with white particles or black particles. As above, three neighboring cells form one pixel. In this method, similarly to the method which employs chromatic particles, there is a problem in that either white display or black display is not achieved with an appropriate density.
As described above, because, in essence, only two colors can be displayed at a single display element in the above-described conventional techniques, there is a problem in that display quality for either white display or black display deteriorates when multi-color display is implemented.